Ordinarily, each unit pixel of an active matrix organic electroluminescent display device comprises a switching transistor, a driving transistor, a capacitor and a light emitting element. A common power supply (Vdd) is supplied to the driving transistor and the capacitor from the power supply line. A common power supply should be uniformly supplied to a plurality of pixels arranged in a matrix form so as to obtain uniform luminance, since the power supply line plays a role in controlling an electric current flowing to the light emitting element through the driving transistor. Referring to the following appended drawings, prior art is now described.
FIG. 1 is a cross sectional view illustrating a conventional organic electroluminescent display device. Referring to FIG. 1, an activation layer 120, formed of polysilicon, is formed on a buffer layer 110 which is formed on insulating substrate 100.
Then, a gate electrode 140 is formed by depositing gate insulating layer 130 and gate metal on the front side of the insulating substrate 100 and patterning the gate metal.
Source region 121 and drain region 125 are formed by doping certain impurities in the activation layer 120 by using a mask after forming the gate electrode 140. A region between the source region 121 and the drain region 125 in the activation layer 120 functions as a channel region 123.
Afterward, contact holes 151, 155 for exposing a part of the source region 121 and drain region 125 are formed by depositing an interlayer insulating layer 150 on the source region 121 and drain region 125 and patterning the interlayer insulating layer 150. Source and drain electrodes 161, 165 are formed by depositing a metal layer on the front side of the insulating substrate 100 and photolithgraphing the metal layer. Any one electrode in the source and drain electrodes 161, 165, such as, for example, the source electrode 161, functions as a power supply line.
A via hole 175 for exposing a part of the drain electrode 165 is formed on the passivation layer 170 after forming a passivation layer 170 on the front side of the insulating substrate 100 including the source and drain electrodes 161, 165.
An anode electrode 180 consisting of a reflective film 181 and a transparent electrode 183 is formed by patterning the deposited metal and transparent conductive material after depositing a metal, such as Ag and Al, having a superior reflectivity to that of the insulating substrate 100, on the via hole 175 and depositing a transparent conductive material, such as ITO and IZO, on the deposited metal.
An organic emitting layer and a cathode electrode are formed afterward, although they are not illustrated on drawings.
A power supply line is ordinarily formed using source and drain electrodes 161, 165 in the foregoing conventional organic electroluminescent display device. However, the conventional organic electroluminescent display device has problems in that MoW, mainly used as the source and drain electrodes 161, 165, has a high voltage drop (IR drop) due to high resistance, and a short may be generated between adjacent wirings when the source and drain electrodes 161, 165 are used as a power supply line.